1. Field of the Invention
This invention relates to a fuel injection system adapted to apply swirling energy to a fuel and supply the resultant fuel to a combustion chamber of an internal combustion engine, such as an automobile engine.
2. Description of the Related Art
Fuel injection systems utilizing the techniques for providing a fuel injection port-carrying valve seat in an outlet of a cylindrical valve casing having a valve body, such as a needle valve and a ball valve therein; turning by a swirler a fuel supplied from the outside; and supplying the resultant fuel to the fuel injection port have heretofore been known from Japanese Patent Laid-Open Nos. 47208/1998 and 205408/1998. According to these techniques, a communication passage between the fuel swirler and fuel injection port is opened and closed by disengaging and engaging a part of a free end portion of the valve body and a part of the valve seat from and with each other. Let S1 and S2 equal a minimum cross-sectional area of a clearance between the valve body and valve seat in the condition in which this communication passage is fully opened, and an area of the cross section of the fuel injection port which is perpendicular to the axis thereof, respectively. A flow rate of the fuel then becomes higher in proportion to S1 and S2.
When the minimum cross-sectional area S1 is larger than the cross-sectional area S2 of the fuel injection port, a fuel having a small amount of swirling energy is injected in large quantities from the fuel injection port in an initial period of a fuel injection operation. Since this fuel has a small amount of swirling energy, the diffusivity of fuel spray and the atomization of the fuel are insufficient, so that the combustibility of the fuel in a cylinder of an engine is deteriorated. Conversely, when the minimum opening area S1 is smaller than the cross-sectional area S2, this problem is solved or lightened. However, when S1 is excessively smaller than S2, a flow resistance of the fuel in the communication passage is high, and this causes the swirling energy applied to the fuel by the fuel swirler to be alleviated, a scatter of an angle of spray to increase or the diffusivity of fuel spray and the atomization of the fuel to become insufficient, and thereby the combustibility of the fuel in a cylinder of the engine to be deteriorated.
The fuel having swirling energy flows through the fuel injection port not over the whole of its cross section S2 but mainly over the portion of a cross section thereof which is near an inner surface of the fuel injection port, so that a void occurs in an inner portion of the fuel injection port. Japanese Patent Laid-Open No. 47208/1998 discloses the techniques for setting S2 larger than S1 for the purpose of stabilizing a flow of the swirling fuel with the void retained but this publication does not refer to the above-mentioned problems occurring when S1 is excessively smaller than S2. On the other hand, Japanese Patent Laid-Open No. 205408/1998 discloses in contrast with Japanese Patent Laid-Open No. 47208/1998 the techniques for setting S2 smaller than S1.
The present invention has been made in view of the above-mentioned various problems in this technical field and the present condition of the related art, and provides a fuel injection system capable of holding down a decrease in the swirling energy of the fuel and improving the degree of atomization and combustibility of the fuel.
The fuel injection system according to the present invention is (1) a fuel injection system including a cylindrical fuel swirler having plural swirl grooves, a valve seat engaged with a swirl groove-carrying surface of the fuel swirler and having a fuel injection port, an annular fuel swirl chamber formed between the fuel swirler and valve seat and communicating with the swirl grooves and fuel injection port, and a valve body adapted to be moved forward and backward in a cylindrical hole of the fuel swirler in the axial direction thereof and thereby engaged with and disengaged from the valve seat to cause a communication passage between the fuel swirl chamber and fuel injection port to be closed and opened, wherein a minimum cross-sectional area S1 of a clearance between the valve body and valve seat in the condition in which the communication port is fully opened being smaller than an area S2 of the cross section of the fuel injection port which is perpendicular to the axis thereof, and larger than an average area S3 of the cross section of the fuel injection port which is perpendicular to the direction in which a fuel flow advances.
(2) A fuel injection system according to (1) above, in which the fuel swirl chamber is formed so as to be surrounded by walls of the fuel swirler, valve body and valve seat.
(3) A fuel injection system according to (1) above, in which the fuel swirl chamber is formed to a circular annular shape, the swirl grooves extending in a tangential direction of the fuel swirl chamber.
(4) A fuel injection system according to (1) above, in which surfaces of the fuel swirler and valve seat at which these parts contact each other are inclined with respect to the axes thereof.
(5) A fuel injection system according to (4) above, in which an angle of inclination of the mentioned surfaces with respect to the mentioned axes is not smaller than 45xc2x0 and smaller than 90xc2x0.
(6) A fuel injection system according to (1) or (4), in which the average cross-sectional area S3 is determined by using the following equation:
S3=(xcfx80/4){De2xe2x88x92Q2 sin2 "THgr"Di2xcfx81/(2gPA2)}
wherein
De: an inner diameter (m) of the fuel injection port,
Q: a static flow rate (m3/s) of a fuel supplied to the fuel swirler,
A: a total cross-sectional area (m2) of the swirl grooves,
Di: a length (m) two times as large as an offset amount of the center line of the swirl grooves with respect to the center of the fuel swirl chamber,
"THgr": an angle (xc2x0) of surfaces of the valve seat and fuel swirler at which these parts contact each other with respect to the axes thereof,
g: gravitational acceleration (m/s2)
P: pressure (kgf/m2) of the fuel supplied to the fuel swirler, and
xcfx81: density (kg/m3) of the fuel.
(7) A fuel injection system according to (1) above, in which the swirl grooves have a non-square cross-sectional shape, the volume per unit length of each of the swirl grooves of groove bottoms or the portions of the grooves which are in the vicinity of the groove bottoms being smaller than that per unit length of each of the grooves of upper portions of the grooves.